Liquefied natural gas (LNG), which is one of liquefied gases, is a fossil fuel buried underground and is formed by changing a natural gas, a main ingredient of which is hydrocarbons, into an extremely low temperature liquid state through pressurizing and cooling processes. Since a liquefied gas has a significantly reduced volume compared with a gaseous state, transportation and storage thereof are relatively easy, and for example, it is possible to transport the liquefied gas to a consumption place at a long distance using a dedicated carrying vessel, etc. provided with a particularly manufactured quay capable of maintaining an extremely low temperature state.
A transportation apparatus, which allows such a liquefied gas to flow into the quay for shipping or loading the liquefied gas or to flow outside the quay for unloading, is provided in the quay. Such a transportation apparatus is generally formed of one or more transportation pipes and includes a pump device for moving the liquefied gas into or from the pipes. Korean Patent Publication No. 10-2012-0013255 discloses an example of the transportation apparatus.
However, during a typical transportation process, since a flow rate or speed of a liquefied gas rapidly changes, a pressure inside the transportation pipes drops and the liquefied gas boils off, thereby excessively generating boil-off gas. Such limitation may further increase when the transportation pipes are vertically installed in such a way that the liquefied gas rapidly drops from tops of the pipes in the direction of gravity.
Also, the boil-off gas may occur when a liquefied gas which flows at a high speed is rapidly discharged to a broad space inside the quay with a low pressure. Accordingly, it is necessary to develop an apparatus capable of being applied to a liquefied gas transportation process to minimize the occurrence of boil-off gas.